1. Field of the Invention
The present invention relates to devices and methods for detecting leaks in test subjects and more specifically, to leak detection systems utilizing holography for locating and measuring leaks in rocket motors.
2. Description of the Prior Art
Most rocket engines comprise a myriad of interconnected ducts, manifolds and chambers which convey highly combustible fluids under extreme temperatures and pressures. A leak in any fluid passage, or in any connection therebetween is often hazardous and sometimes catastrophic. Great attention has therefore been directed towards finding ways to check rocket engines for leaks, particularly methods which can be conducted expediently and economically during the manufacture and check-out of the engines.
The most commonly used test for detecting leaks in rocket engines is the soap-bubble test, whereby films of soap solution are applied about preselected locations on a subject engine. As the engine is charged with purging fluid, any gas leaking from the engine forms tell-tale soap bubbles. However, it has been found that this method is very disadvantageous because it can be applied only to a few accessible portions of the rocket motor and is so time-consuming that even it it could be more universally applied, its application to all of the hundreds of joints, welds and brazes on an engine would be prohibitive. In addition, the method requires the application of a soap film upon test subject, which application disturbs surface finish.
Another device for leak testing rocket engines comprises a bag for encapsulating the powerhead of the engine and means for directing an effluent to pass through the bag and then into a spectrometer while the engine is being purged. Any leakage from the engine is carried by the effluent to the spectrometer where it is detected. This device is disadvantaged, however, by its limited ability to detect only the presence of a leak without any indication as to its location. Moreover, the device requires the attachment of the bag to the engine, which is a cumbersome and time consuming step. In addition, the seal between the bag and the engine itself can be a source of leakage which can affect the results obtained from the spectrometer.
Other prior devices used for detecting leaks in rocket engines include helium spectrometric leak detectors, ultrasonic leak detectors and thermo-differential leak detectors. However, the spectrometric and thermo-differential devices suffer the disadvantage that they have little or no capability for detecting leaks unless they are placed in close proximity to the suspected situs of each leak. Similarly, the usefulness of the ultrasonic devices is hampered by their requirement that they be properly aimed towards each leak, individually. Because all of these devices must be applied to all of the suspected situses, one at a time, their use in connection with complicated subjects, such as rocket engines, exacts unacceptably large amounts of time and effort. Consequently, great interest has remained in the discovery of a device which is capable of indicating in an expedient fashion both the location and magnitude of all leaks in a given test subject, even when the test subject is quite complicated.